Signal modulation



June 19, 1934. w gusc a c I 1,963,117

SIGNAL MODULATION Filed Jan. 21, 1952 .1. I I f I 2% I I 8,; ENE 7 III INVENTOR WERNER BU SC BECK ATTbRNEY Patented June 19, 1934 UNITED STATES,

SIGNAL MODULATION Werner Buschbeck, Berlin, Germany, assignor. to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application January 21, 1932, Serial No. 587,843

r In Germany January 24, 1931 4 Claims.

Thisinvention relates to a modulating circuit and in particular to grid direct current modula-f tion wherein the oscillations to be modulated are passed through a thermionic repeater in which modulation is accomplishedby varying the potential of the control grid and/or the flow of rectified direct current in the control grid-cathode circuit at signal frequency.

A particular object of the present invention is to provide a novel modulating scheme of the above type in which novel means is provided for obtaining eflicient modulation of the carrier without distortion.

The novel features of the invention have been pointed out with particularity in the claims appended hereto.

The nature of the invention and the operation of the same will be understood by the following detailed description thereof and therefrom when read in connection with the drawing, in which:

Figure 1 shows modulators of the type involved and is used for the purpose of illustrating the detectors, the object of which the present invention is to overcome; while,

Figure 2 shows a modulator of the grid direct current type arranged in accordance with applicants novel invention.

It is known in the prior art that normal griddirect current modulation is made practicable in tubes depending for their operation upon secondary electron emission from the grid by the addition of an auxiliary direct current. One embodiment of a circuit scheme of this kind is shown in Fig. 1. This arrangement could also be employed to great advantage in tubes in which the grid direct current has been corrected for the purpose of improving the modulation characteristic or curve in its bottom part. The normal grid direct current, as will be noted, does not decrease linearly with growing negative grid potential of the oscillator tube, but rather at a far higher power so that in the bottom end of the characteristic (in telephony Work), in the absence of an auxiliary direct current the modulator tube must be blocked rather extensively to result in an adequately high grid biasing potential of the oscillator. But if an auxiliary electro-motive force Ez is present and is in series with a resistance Rz ;(see Fig. 1) connected in parallel to the modulator tube, with the polarity being sochosen that the negative end of the electro-motive force is united with the filament of the modulator tube, and having a value higher than that of the max- .imum grid direct current potential Eg likely to arise there will invariably flow a supplementary direct current in the sense of the normal grid direct current through the modulator tube, evenin the presence of grid biasing potentials Eg at which the grid direct current of the modulated tube has already been reduced to zero value. Now, this supplementary direct current is superfluous and undesirable only for the positive values of the telephony current since it increases still further the grid direct current which normally is quite ample for positive values of the telephone current.

According to the present invention the shape of the telephone characteristic curve, that is, the curve representing the modulating currents, can be influenced, not only in the lower end, by replacing the constant resistance Rz included in the circuit of the auxiliary electromotive force by the impedance between the anode and cathode of a'tube, as shown in Figure 2, and controlling the impedance of this auxiliary tube in accordance with variations in? the grid direct current of the main transmitter tube which flow through the anode to cathode impedance of the modulator tube and a resistance placed in series therewith. The grid of this supplementary modulator tube, if desired, is connected, as shown, by way of a constant electromotive force with a resistance connected in series with the anode to cathode impedance of the modulator tube in the grid direct current circuit. If the grid direct current is large then the additional direct current is cut ofi or diminished, and vice versa. By suitable selection of the working point in the grid direct current and supplementary modulator tube, or the parallel and series connection of constant resistances relative to the supplementary modulator tube the shape of the modulation characteristic can be influenced to the highest possible extent.

I claim:

1. A thermionic tube having its input electrodes energized by high frequency oscillations, means for modulating the oscillations in said thermionic relay tube including, a modulator tube having its anode to cathode impedance connected between the control grid and cathode impedance of said relay, a resistance for applying a direct current potential between the anode and cathode electrodes of said modulator tube, and means connected with the anode of said modulator tube for determining the amount of curto g rent flowing therein due to said applied potential comprising a thermionic tube having its anode to cathode impedance in series with said potential applying means and its control grid connected with the anode of said modulator tube.

2. A thermionic relay having its input electrodes energized by high frequency oscillations, a circuit for modulating the oscillations in said relay at signal frequency including, a modulator tube having its cathode connected to the control grid of said relay tube and its anode connected to the cathode of said relay tube, a source of modulating potentials connected between the control grid and cathode of said modulator tube, an auxiliary tube having its anode to cathode impedance connected by way of a source of direct current potential between the anode and cathode of said modulator tube, and a connection between the control grid of said auxiliary'tube and the anode of said modulator tube.

3. A thermionic relay adapted to repeat high frequency oscillations and means for modulating the oscillations repeated in said tube including,

a modulator tube having its anode to cathode nected between the control grid and cathode of said modulator tube, an auxiliary thermionic tube having its anode connected by way of a source of direct current potential to the cathode of said modulator tube, means for connecting the cathode of said auxiliary tube to the cathode of said repeater tube and to the anode'oaf said modulator tube, and a connection between the anode of said modulator tube and the control grid in said auxiliary tube.

4. A modulator circuit including, a thermionic tube having its input electrodes connected with a source of high frequency oscillations, at modulator tube having its cathode connected to the control grid of said first tube and its anode connected to the cathode of said first tube, a source of modulating potentials connected between the control grid and cathode of said modulator tube, and means for insuring linear modulation by controlling the direct current potential applied to the input electrodes of the first tube comprising a controllable variable impedance connected by way of a source of potential between the control grid and cathode of said first named tube, said variable impedance being controlled by the current flow in said modulator tube.

WERNER BUSCHBECK. 

